Carbon nanotubes are generally elongated hollow, tubular bodies with a linear graphene structure. They are typically only a few atoms in circumference and may be single-walled or multi-walled. Carbon nanotubes are recognized as possessing excellent mechanical, chemical, electrical and thermal properties and have potential uses in a diverse number of applications from sports equipment to electroconductive paint.
One use of carbon nanotubes has been to add them to polymer matrices as separate fillers or as reinforcing agents. However, the more recent development of attaching polymers to carbon nanotubes to form polymer-carbon nanotube composites offers exciting new potential uses. By chemically or physically linking the nanotubes to the polymer chains, the resultant composites benefit from the mechanical, thermal and electrical properties of the carbon nanotubes to provide multifunctional new lightweight materials. Potential uses of such materials include structural or other parts in the aeronautic, aerospace or automotive industries, sports equipment etc.
Attempts to make such polymer-carbon nanotube composites include chemically modifying the ends or the side walls of carbon nanotubes with functional groups (known as functionalization or derivatization), which then react to form, or to link with, polymer chains.
U.S. Pat. No. 7,250,147 describes a process for the chemical modification of carbon nanotubes and their chemical incorporation into polymers. The process involves the functionalization of the sidewalls and the ends of multi- and single-wall carbon nanotubes with diazonium species using an electrochemical process. The functional group is then actively involved in a polymerisation process which results in a polymer composite material in which the carbon nanotubes are chemically involved. Electrochemical processes/diazonium species for functionalizing carbon nanotubes have the disadvantage of delicateness of handling and diazonium synthesis which involve the use of compounds such as tetrafluoroborate.
US 2006/0142466 describes a process for growing polymer chains via polymerisation from the sidewalls of functionalized carbon nanotubes, where the nanotube sidewalls are functionalized with an aryl halide or a specie comprising a nucleation site operable for anionic or ring opening polymerisation. The functionalization step is as described in U.S. Pat. No. 7,250,147 and involves an electrochemical process.
US 2004/0265755 describes a method of producing a polymerized carbon nanotube composite including modifying surfaces of the carbon nanotubes with an oxirane or an anhydride group and heat curing over a substrate. The carbon nanotubes are carboxylated by acid reflux methods before functionalizing with the oxirane or anhydride groups.
US 2006/0249711 describes processes for producing polymers containing functionalized carbon nanotubes where the carbon nanotubes are functionalized by sulfonation, electrophilic addition to deoxygenated carbon nanotube surfaces or metallation (as described in U.S. Pat. No. 6,203,814). However, these functionalization processes are only directed toward polycondensation or polyaddition polymerisation.
US 2006/0166003 describes processes for producing epoxy polymer-carbon nanotube composites involving the attachment of functional groups to the sidewalls or end caps of carbon nanotubes and the subsequent reaction of these functional groups with either epoxy precursors or the curing agents. The sidewall functional groups are formed by fluorination which yield sidewall functionalized fluorinated carbon nanotubes which typically takes place at temperatures of between 150-325° C. The fluorinated carbon nanotubes must then go through a second reaction step to yield a functional group which can be chemically linked to a polymer chain. This renders the method complex and time consuming and so difficult to step-up.
Therefore, it is desired to overcome or reduce at least some of the above-described problems.